TBK1 is a serine/threonine kinase with diverse roles in cancer, inflammation, and the host-pathogen response. Shen, R. R. and W. C. Hahn (2011) Oncogene 30(6): 631-641. TBK1 activates its substrates IRF3 and IRF7 transcription factors by direct phosphorylation of specific sites that induces their localization to the nucleus to drive transcription of type I IFN genes (Sankar, S., H. Chan, et al., (2006) Cell Signal 18(7): 982-993). In addition, NFkB activation can be bolstered by the kinase activity of TBK1 phosphorylating the inhibitors of NFkB, which enables activation of the canonical or non-canonical NFkB transcription factors.
TBK1 has been implicated as being a key gene required for KRAS-dependent cancers, required for HER2+ breast cancers, and contributing to the acquisition of resistance to erlotinib. Depletion of TBK1 by shRNA results in synthetic lethality with KRAS-dependent cancer cell lines and xenograft models (Barbie, D. A., P. Tamayo, et al. (2009) Nature 462(7269): 108-112) and TBK1 is required for RAS-mediated transformation of murine embryonic fibroblasts (Ou, Y. H., M. Torres, et al. (2011) Mol Cell 41(4): 458-470). TBK1 is downstream of RAS and elicits its oncogenic properties via the RALB-NFkB and AKT pathways (Chien, Y., S. Kim, et al. (2006) Cell 127(1): 157-170). In addition, TBK1 directly phosphorylates AKT at S473 and results in the downstream activation of the mTORC1/2 pathway (Ou, Y. H., M. Torres, et al. (2011) Mol Cell 41(4): 458-470). TBK1 was also identified as being important for the survival of HER2+ breast cancer cell lines via an shRNA kinome screen and showed combination effects with the EGFR/HER2 kinase inhibitor, lapatinib (Deng, T., J. C. Liu, et al. (2014) Cancer Res 74(7): 2119-2130). Additionally, integrin alphaVbeta3 was identified as a marker of cells that are resistant to EGFR therapies and have stem-like properties. The signaling cascade required for the survival of these cells was attributed to KRAS-TALB-TBK1-NFkB axis and inhibiting TBK1 was sufficient to block the survival of these cells. Seguin, L, S. Kato, et al. (2014), Nat Cell Biol 16(5): 457-468.
IKKε is a serine/threonine kinase and its gene amplifications have been identified in up to 30% of breast cancers. Depleting IKKε in cell lines with shRNA that have these amplifications results in their decreased viability (Boehm, J. S., J. J. Zhao, et al. (2007) Cell 129(6): 1065-1079). Overexpression of IKKε in ovarian cancer has been demonstrated to mediate resistance to cisplatin and is a poor prognostic factor (Guo, J. P., S. K. Shu, et al. (2009) Am J Pathol 175(1): 324-333).
TBK1 and IKKε are also both implicated in inflammatory responses and associated disorders. IKKε has been shown to be involved in manifestations of rheumatoid arthritis (RA) that include extracellular matrix destruction, synovial inflammation, and activation of the innate immune response (Sweeney, S. E., D. Hammaker, et al. (2005) J Immunol 174(10): 6424-6430). IKKε and IRF3 protein levels are increased in the synovium of RA patients and mice deficient in IKKε show reduced clinical signs of arthritis in a collagen-induced arthritis model as well as associated reduction of inflammation and erosion. Corr, M., D. L. Boyle, et al. (2009), Ann Rheum Dis 68(2): 257-263. Other inflammatory disorders that manifest as a result of Type I IFN response and upstream activation of TLR3/TLR4 or cytosolic nucleic acid sensors are likely to also rely on a TBK1/IKKε signaling axis to initiate and maintain their pathogenic state such as Sjogrens syndrome, inflammatory bowel disease (IBD), chronic obstructive pulmonary disease (COPD), systemic lupus erythematosus (SLE), dermatomyositis, polymyositis, systemic sclerosis. Baccala, R., K. Hoebe, et al. (2007), Nat Med 13(5): 543-551. Furthermore, both TBK1 and IKKε have been shown to play a role in maintaining macrophages in an activated state in response to IFN. Solis, M., R. Romieu-Mourez, et al. (2007) Eur J Immunol 37(2): 528-539.
In addition to inflammation and cancer, IKKε is implicated in obesity, type 2 and insulin resistance. Mice deficient for IKKε are protected from obesity induced by a high-fat diet, hepatic steatosis, insulin resistance, and chronic inflammation of the liver and fat. Chiang, S. H., M. Bazuine, et al. (2009) Cell 138(5): 961-975. Consistent with this, high levels of NFkB activation have been seen in the liver, adipocytes, and adipose tissue resident macrophages as well as increase levels of IKKε over healthy mice. Treatment with a kinase inhibitor to TBK1/IKKε improved obesity-related metabolic dysfunction in mice fed a high fat diet (Reilly, S. M., S. H. Chiang, et al. (2013) Nat Med 19(3): 313-321).
Accordingly, there is a need for inhibitors of the kinase activity of TBK1 and/or IKKε for treating cancers, inflammatory, and metabolic disorders that may have an active TBK1 and/or IKKε pathway.